Additive Manufacturing Special Report - November 2023 - 18

TECH BRIEFS
Assembling Matter in 3D Using Sound Waves for 3D Printing
The technology uses multiple acoustic holograms to generate pressure fields with which solid
particles, gel beads, and even biological cells can be 3D printed.
Max Planck Institute for Medical Research and the Heidelberg University, Germany
A
team of researchers from
Heidelberg University and Max
Planck Institute for Medical Research
have created a new technology to
assemble matter in 3D. Their concept
uses multiple acoustic holograms to
generate pressure fields with which
solid particles, gel beads, and even
biological cells can be printed. These
results pave the way for novel 3D cell
culture techniques with applications
in biomedical engineering.
Additive manufacturing, or 3D
printing, enables the fabrication of
complex parts from functional or
biological materials. Conventional 3D
printing can be a slow process, where
objects are constructed one line
or one layer at a time. Researchers
now demonstrate how to form a 3D
object from smaller building blocks
in just a single step. " We were able
to assemble microparticles into a
three-dimensional object within a
single shot using shaped ultrasound " ,
said Kai Melde, Postdoc in the group
and first author of the study. " This
can be very useful for bioprinting.
The cells used there are particularly
sensitive to the environment during
the process, " added Peer Fischer,
Professor at Heidelberg University.
Sound waves exert forces on
matter - a fact that is known to
any concert goer who experiences
the pressure waves from a
loudspeaker. Using high-frequency
ultrasound, which is inaudible to
the human ear, the wavelengths
can be pushed below a millimeter
into the microscopic realm, which
is used by the researcher to
manipulate very small building
blocks, like biological cells.
In their previous studies Peer
Fischer and colleagues showed
how to form ultrasound using
acoustic holograms - 3D-printed
18 NOVEMBER 2023
The use of sound waves to create a pressure field to print particles. (Image: MPI for Medical Research,
Heidelberg University/Kai Melde)
plates, which are made to encode
a specific sound field. Those sound
fields, they demonstrated, can
be used to assemble materials
into two-dimensional patterns.
Based on this the scientists
devised a fabrication concept.
With their new study the team
was able to take their concept a
step further. They capture particles
and cells freely floating in water
and assemble them into threedimensional
shapes. On top of
that, the new method works with a
variety of materials including glass or
hydrogel beads and biological cells.
First author Kai Melde said, " the
crucial idea was to use multiple
acoustic holograms together and
form a combined field that can catch
the particles. " Heiner Kremer, who
wrote the algorithm to optimize
the hologram fields, added, " The
digitization of an entire 3D object
into ultrasound hologram fields is
computationally very demanding
and required us to come up with
a new computation routine " .
The scientists believe that their
technology is a promising platform
for the formation of cell cultures
and tissues in 3D. The advantage
of ultrasound is that it is gentle for
using biological cells and that it can
travel deep into tissue. This way it
can be used to remotely manipulate
and push cells without harm.
For more information, contact
Elisabeth Fuhry at elisabeth.fuhry@
mr.mpg.de; +49-6221-486-650.
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Additive Manufacturing Special Report - November 2023

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